HR: 1340h
AN: A33D-1535    [Abstracts]
TI: Detection of NO3 and N2O5 by thermal dissociation with LIF detection of NO2 and NO3
AU: * Rollins, D W
EM: ice@berkeley.edu
AF: Department of Chemistry, University of California Berkeley, B47 Hildebrand University of California Berkeley, Berkeley, CA 94720,
AU: Fry, J L
EM: fry@berkeley.edu
AF: Department of Chemistry, University of California Berkeley, B47 Hildebrand University of California Berkeley, Berkeley, CA 94720,
AU: Wooldridge, P J
EM: pjwool@berkeley.edu
AF: Department of Chemistry, University of California Berkeley, B47 Hildebrand University of California Berkeley, Berkeley, CA 94720,
AU: Cohen, R C
EM: rccohen@berkeley.edu
AF: Department of Chemistry, University of California Berkeley, B47 Hildebrand University of California Berkeley, Berkeley, CA 94720,
AB: The nitrate radical, NO₃, is believed to be an important sink of anthropogenic alkenes and many unsaturated biogenic volatile organic compounds. The chemistry of NO₃ and its reservoir N₂O₅ are also effective NO_x sinks due to these same oxidation reactions which produce organic nitrates and HNO₃ and to heterogeneous chemistry on aerosol surfaces producing HNO₃. Measurements of NO₃ and N₂O₅ by 10 different instruments were obtained simultaneously during the 2007 NO₃/N₂O₅ intercomparison at the SAPHIR (Simulation of Atmospheric PHotochemistry In a large Reaction Chamber) chamber in Juelich, Germany. Here we compare our measurements of NO₃ and N₂O₅ by two independent Thermal Dissociation - Laser Induced Fluorescence (TD-LIF) techniques that employ detection of NO₃ and NO₂. In one instrument NO₃ is detected by electronic excitation at 662nm with an inexpensive, low-power (30mW) diode laser followed by collection of red shifted fluorescence (700-750 nm). N₂O₅ is detected in this instrument by thermal dissociation to NO₃ and NO₂ in a second heated inlet at 200°C followed by LIF detection of NO₃. N₂O₅ is calculated by subtracting the two signals. In this instrument detection limits of 74 pptv and 38 pptv have been achieved (signal/noise = 2) for NO₃ and the sum of NO₃ + N₂O₅ respectively with 5 minutes of signal averaging. In a second instrument NO₂ is excited with a diode laser at 408nm and fluorescence longer than 650nm is collected. N₂O₅ is detected in this instrument by thermal dissociation to NO₂ using a heated inlet held at 180C. NO₃ has also been observed to be detected in this instrument using a heated inlet at 600°C, with decreased efficiency relative to the NO2 fragment from N₂O₅. In this paper, details of the instrument design and calibration, discussion of the inlet transmission efficiency and the mechanism for NO₃ detection in the NO₂ LIF system are discussed.
DE: 0365 Troposphere: composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting